Why does my laptop make a constant bell sound?

I have an HP Pavillion tx1000 and a dv6000. Once in a while it would make a constant bell sound. It's hard to describe.. it's like the sound the hp makes when you enter an incorrect password or something. But this sound would go on forever (literally) until the laptop is rebooted. None of my other brands of laptops has ever had this problem, it's only with both the hp's. Why does it do that? and how can I stop it without rebooting? Please help me stop that annoying ringing =[ please and thank you!